Read this before you sell or recycle your computer!

Last month, researchers in Britain decided to find out if people left anything behind when they sold or donated their old computer. They bought 300 used machines in several countries and from a number of sources, including eBay.

What did they find? About one-third still contained personal data on the hard drives, data that was located with just a little digging. Among the items rooted out: the test-launch information for THAAD ground-to-air defense missiles; medical records from hospitals; Social Security numbers; and proprietary commercial documents, such as business plans.

The disturbing conclusion: Even large organizations, which have legal obligations to protect their data, are sometimes lax about removing them thoroughly from discarded computers.

What about average home users?

The biggest mistake they make, experts say, is to assume that files are gone from the hard drive once they’ve been placed in the trash bin and deleted. “The actual data remains intact on the hard drive. There are programs available designed to find this data and easily re-create the original information,” explains Michael Helander, a spokesman for Lavasoft, a Swedish software security firm, in an e-mail.

To really erase all personal data from a hard drive, users have two choices: The first involves software; the second, elbow grease.